This thread contains the known issues with plugins and themes found in 3.6. Please read this WHOLE topic and come back and check again later, as it will be updated.

Remember to be calm, be patient and be respectful. Volunteers are out here to TRY and help you, but we need your help too. ALL forum rules still apply. You are just as important as everyone else.

If your post doesn't show up right away, please be patient. With the higher than normal post volume, more people get erroneously flagged as spam. We're working hard to keep the queue clear, but making multiple posts slows us down, as we have to go back and check if you already posted. Post one. If it shows up as 'Anonymous', we'll fix it for you. Just wait.

Do use proper capitalization (in titles or body). Punctuate your sentence properly and humanely, it helps us read.

Do use descriptive subject lines ("All permalinks broken since 3.6" instead of "Augh! Help ASAP! This version is terrible!")

Do be patient. We know it sucks to be down, but we delete bumps on sight.

Do make your own topic unless you are using the same version of WordPress on the same physical server hosted by the same hosts with the same plugins, theme and configurations as the original poster (I know it's weird, but it will be easier for us to help YOU that way)

Do mark your topic as resolved when it's fixed so we know not to come looking there anymore.

Do remember you're not alone.

If you're upgrading from an older version of WordPress, you may want to read lists for 3.1, 3.2, 3.3, 3.4, and 3.5. There are known issues with older themes and plugins, and they may not have been corrected.

Also keep in mind that not liking the direction of WordPress's Admin Design does not a bug make. If you don't like a feature, please don't make a series of posts complaining about it. Look and see if someone already did, and post there, or consider joining the process earlier on (like in Beta or even test via SVN). What you're seeing today is the result of months of work and testing, and unless something is outright broken, it's highly unlikely to be changed.

Go to your own install's about page - http://example.com/wp-admin/about.php - to see what's new.

And then make sure you've tried...

flushing any caching plugins you might be running, as well as server and/or browser caches.

deactivating all plugins (yes, all) to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s). If you can't get into your admin dashboard, try resetting the plugins folder by FTP or PhpMyAdmin (read "How to deactivate all plugins when you can't log in to wp-admin" if you need help). Sometimes, an apparently inactive plugin can still cause problems. Also remember to deactivate any plugins in the mu-plugins folder. The easiest way is to rename that folder to mu-plugins-old

switching to the Twenty Twelve theme to rule out any theme-specific problems. If you can't log in to change themes, you can remove the theme folders via FTP so the only one is twentytwelve. That will force your site to use it.

manually upgrading. When all else fails, download a fresh copy of the latest.zip file of 3.6 (top right on this page) to your computer, and use that to copy up. You may need to delete the wp-admin and wp-includes folders on your server. Read the Manual Update directions first.

Twenty Thirteen: We’re shipping this year’s default theme in our first release of the year. Twenty Thirteen is an opinionated, color-rich, blog-centric theme that makes full use of the new Post Formats support.

Audio/Video: You can embed audio and video files into your posts without relying on a plugin or a third party media hosting service.

Just as many people hated the old ones. Hating the new menus is not a bug.

TwentyThirteen is a terrible default theme!

It's just a theme. If you don't like it, don't use it. We know not everyone will like it, and that's okay. That means that things like 'The video title is UNDER my video!' is not a bug, it's a design choice.

Not a bug. This is intentional. Going forward we'll want a better filter to let people turn it off though, so keep tabs on trac ticket 24551 is open. For now, you can use this filter to warn people, but not prevent editing:

Plugins and themes which use their own jQuery without properly compensating for WP's will break. Again. jQuery was upgraded in 3.6, so even though this should be much less of a problem, please take note. (Plugin and Theme Devs - Please stop using your own version of jquery!)

Plugins and themes that happen to be using jQuery.BlockUI may have an interesting error where they get a popup saying that they need to use jQuery later than v 1.2.3 even though WordPress is using 1.10.1

This is caused by math not acting the way humans assume it will. In older versions of the jQuery.BlockUI code used by plugins there is a little 'buglet' - the code tests for versions BUT drops the trailing '0', so instead of asking is 1.10 greater than 1.2, it tests if 1.1 is greater than 1.2, and so it fails.

To fix this, you need to update the theme/plugin having the issue. From ChipsOnFire, here's his solution:

My plugin used a file called wf-an-jqery-plugins.js. Inside that file was a chunk of jQery.BlockUI code that said it was v2.39.

I went to the following link for the latest jQuery.BlockUI code (v2.64) and then just replaced the v2.39 code in that plugin file with the code from this link. Hey presto, it all works again: http://malsup.github.io/jquery.blockUI.js

This is not something WP did wrong, it's just how computers sometimes decide to order numbers in non-sensible ways. The reason this wasn't caught in testing was apparently none of the beta testers were using old BlockUI code.

Audio/Video Plugins

Since WordPress now auto-emebeds audio and video (and uses the [audio] and [video] shorttags), any plugin or theme that adds those in may conflict.